We present an untriggered search for optical bursts with the ROTSE-I telephoto array .
Observations were taken which monitor an effective 256 square degree field continuously over 125 hours to m _ { ROTSE } = 15.7 .
The uniquely large field , moderate limiting magnitude and fast cadence of \sim 10 minutes permits transient searches in a new region of sensitivity .
Our search reveals no candidate events .
To quantify this result , we simulate potential optical bursts with peak magnitude , m _ { p } , at t=10 s , which fade as f = \left ( \frac { t } { t _ { 0 } } \right ) ^ { \alpha _ { t } } , where \alpha _ { t } < 0 .
Simple estimates based on observational evidence indicate that a search of this sensitivity begins to probe the possible region occupied by GRB orphan afterglows .
Our observing protocol and image sensitivity result in a broad region of high detection efficiency for light curves to the bright and slowly varying side of a boundary running from [ \alpha _ { t } ,m _ { p } ] = [ -2.0 , 6.0 ] to [ -0.3 , 13.2 ] .
Within this region , the integrated rate of brief optical bursts is less than 1.1 \times 10 ^ { -8 } ~ { } { s } ^ { -1 } ~ { } { deg } ^ { -2 } .
At \sim 22 times the observed GRB rate from BATSE , this suggests a limit on \frac { \theta _ { opt } } { \theta _ { \gamma } } \lesssim 5 where \theta _ { opt } and \theta _ { \gamma } are the optical and gamma-ray collimation angles , respectively .
Several effects might explain the absence of optical bursts , and a search of the kind described here but more sensitive by about 4 magnitudes should offer a more definitive probe .